1. Field of the Invention
The invention relates to a multi-domain vertical alignment liquid crystal display, and in particular to a pixel structure for a wide viewing angle liquid crystal display capable of improving display quality.
2. Description of the Related Art
In modern thin film transistor liquid crystal displays, characteristics such as high contrast ratio, high luminescence, low color shift, no gray scale inversion, no image retention, high response speed, and wide viewing angle are desirable.
A narrow viewing angle, however, has existed in conventional thin film transistor liquid crystal displays. To increase viewing angle, one technique, dividing liquid crystal into multi-domains where liquid molecules are in various declination directions, has been proposed. Typically, a combination of a protruding portion and a conductive electrode with a slit is utilized in, for example, a multi-domain vertical alignment liquid crystal display. Moreover, the protruding portion and conductive electrode with a slit are disposed respectively on upper and lower substrates, opposing a liquid crystal layer between the substrates, thus the liquid crystal molecules have a pre-tilt angle. The liquid crystal molecules may have various declination directions when a voltage is applied.
FIG. 1 is a plan view of a pixel structure for a conventional multi-domain vertical alignment liquid crystal display. Referring to FIG. 1, one sub-pixel 200 of a conventional multi-domain vertical alignment liquid crystal display comprises protrusion 100 on a color filter substrate, a slit containing conductive electrode 104 on an array substrate. By means of a staggered arrangement of the protrusion and slit, liquid crystal molecules are set in four different declination directions, leading to formation of four different azimuthal angle domains. Thus a wide viewing angle can be achieved. However, as shown in FIG. 1, the width P0′ of the first azimuthal angle domain is equal to the width P0 of the second azimuthal angle domain, thus the azimuthal angle domains on both sides of the protrusion 100 in a sub-pixel are unequal in area. For example, the first 202 and second 204 azimuthal angle domains are unequal in area, the overall display quality may be affected by problems such as color washout and gray scale inversion. FIG. 2 is a diagram showing the relationship of the γ curve vs. the viewing angle for a conventional multi-domain vertical alignment liquid crystal display. As shown in FIG. 2, curves A, B and C denote γ curves at viewing angle 0°, right viewing angle and left viewing angle, respectively. It is Note that curves B and C are far away from each other.
To ameliorate the drawbacks, another technique is proposed, as shown in FIG. 3. In a sub-pixel 200′, each azimuthal angle domain is equal because the areas of azimuthal angle domains are adjusted by means of altering the position of the protrusion 100. The width P2′ of the first azimuthal angle domain 202′, however, is not equal to the width P2 of the second azimuthal angle domain 204′; the width P1 of the third azimuthal angle domain 206′ is not equal to the width P1 of the second azimuthal angle domain 208′. As a result, other problems such as image retention, low response speed and gray scale inversion may occur while the drawbacks are compensated by altering the position of the protrusion 100. Image retention is induced by unstable disconnection lines resulting from various disordering forces among liquid crystal molecules in a sub-pixel when P1≠P1′, P2≠P2′. Low response speed is caused by weaking forces among liquid crystal molecules when P1′ and P2′ are too long.
“Gray scale inversion” occurs because some azimuthal angle domains may be dramatically diminished due to alignment errors when P1 and P2 are too small.
Accordingly, a wide viewing angle liquid crystal display capable of improving display quality is desirable.